Automatic exposure control system



United States Patent [72] Inventor Donald M. Harvey Rochester, N.Y.

[2]] Appl. No. 718,033

[22] Filed April 2, 1968 [45] Patented Dec. 15, 1970 [73] AssigneeEastman Kodak Company Rochester, N.Y. a corporation of New Jersey [54]AUTOMATIC EXPOSURE CONTROL SYSTEM [56] References Cited UNITED STATESPATENTS 3,173,347 3/1965 Stimson et al. 95/1 1.5X 3,465,656 9/1969 Wicket al 95/1 1.5X

Primary ExaminerJohn M. Horan Assistant Examiner-Joseph F. Peters, Jr.Anorneys- Robert W. Hampton and Ronald S. Kareken ABSTRACT: An automaticexposure control system particularly for photographic flash exposureswherein before exposure a low intensity preflash is used to actuate anelectric circuit for setting calibrated exposure control means. Alsodisclosed are means for automatically focusing a camera lens incoordination with the setting of the exposure control means.

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I INVENTOR DONALD M. HARVEY fl w-$1M BY fM a) M ATTORNEYS AUTOMATICEXPOSURE CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to automatic flash exposure controlsystems in photographic cameras.

2. Description of the Prior Art It is well known in photography toutilize automatic exposure control systems when exposure is to be madewith existing light. Such automatic exposure control systems normallyoperate by determining the intensity of the existing illumination with alight responsive element such as a photocell, and adjusting the exposureregulating devices such as the diaphragm according to the light levelindicated. One system comprises adjustment by the deflection of agalvanometer resulting from the change in the electric current of thephotocell circuit. However, these systems are inadequate for flashexposure, since they do not compensate for the intensity of illuminationwhich will be available from the exposure flash. One system forindicating properexposure for flash is described in Stimson, U.S. Pat.No. 3,173,347 which uses an infrared preflash to indicate the combinedambient flash light level resulting from the flash exposure.

SUMMARY OF THE INVENTION The present invention comprises an automaticflash exposure control system wherein a preexposure flash is provided bya low intensity light or electronic flash to initially illuminate thescene to provide information to permit the automatic setting of theexposure controls. A photocell detects the illumination intensity duringthe preexposure flash, the resulting weak signal is amplified, and afilter circuit determines that portion of the total illumination duesolely to the flash. A galvanometer, which measures this signal, in turnadjusts the exposure control device in proportion to the intensity ofthe signal received by the galvanometer. Since the preexposure flash isa known fraction of a higher intensity exposure flash, the resultingexposure control mechanism of the camera is adjusted as a function ofthe circuit to permit the correct amount of light to expose the filmwhen the actual exposure is made with the exposure flash. Furthermore,means may be provided to make any further adjustment necessary tocompensate for high level ambient light, and means are provided foroverriding the automatic flash exposure control means if the ambientlight is of sufficient intensity to make flash exposure unnecessary. Afurther aspect of the invention comprises means for coupling the focusof the camera lens with the flash exposure control system, wherebyfocusing is accomplished in conjunction with the setting of the exposurecontrol means by the preexposure flash.

BRIEF DESCRIPTION OF THE DRAWING -ventional flash embodiments of theinvention;

FIG. 4 shows a viewfinder reticle used in conjunction with anembodimentof the invention;

FIG. 5 shows the circuitry and details of the preferred embodiment ofthe invention; and

FIG. 6 illustrates a further embodiment wherein means are provided forcoupling the camera focus mechanism with the preflash exposure on stem.

2 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, whichschematically shows the invention, an exposure control system accordingto the invention comprises a light measuring circuit including aphotocell or other light responsive element l, a signal amplifier 2, anelectronic signal filter 3, and a switch 10; and the balance of theexposure control system comprises a galvanometer 4, a single vanediaphragm member 5 forming the movable member of the galvanometer andhaving a tapered aperture 8, a portion 8 of which is shown in alignmentwith a camera objective 9, and means for locating the diaphragm member 5relative to the objective 9 comprising a pawl 6 on the member 5 and afixed ratchet 7. Light, having been reflected from the scene illuminatedby a low intensity preexposure flash (not shown) in FIG. 1 is detectedby photocell l. The electrical signal thereby generated is amplified byamplifier 2. Filter 3 segregates the AC portion of the amplified signal,which is that portion of the total electrical signal due solely to thescene illumination caused by the preexposure flash, i.e., the ambientillumination is filtered out. Diaphragm member 5 of galvanometer 4 isdeflected by an amount proportional to the signal it receives, thesignal corresponding to that which would have received had the flashbeen the full intensity exposure flash. This deflection results inmotion of diaphragm member 5 to the left as shown, whereby aperture 8 ispositioned such that a portion 8' of the aperture is located in linewith camera lens 9 to permit the proper amount of light to pass throughobjective 9 to expose properly the film when the camera shutter (notshown) is actuated to make the flash exposure.

The adjustment of the diaphragm as shown is for only one shutter speed,but means may be provided to automatically calibrate the diaphragmsetting for other shutter speeds by any of the known means. Pawl 6 andratchet 7 are provided for holding the diaphragm 5 in the set position.Further means (not shown) are provided for releasing the pawl 6 anddiaphragm member 5 after the exposure is made, or when the setting is nolonger desired. As shown the setting is accomplished by a movement ofthe diaphragm member 5 from right to left, with member 5 being reset bymovement of member 5 to the right until the maximum portion of aperture6 is aligned with objective 9. Furthermore, means may be provided forautomatically overriding the aforementioned flash exposure setting totake into account the intensity of high levels of ambient light. Forinstance, this may be accomplished by closing switch 10 first before orafter the preexposure flash setting is made to permit an adjustment ofthe diaphragm member 5 according to the level of ambient light. Ineither case the pawl and ratchet connection provides that the member 5is set at the smaller aperture determined by the higher level of light.Normally, however, the ambient light intensity is insignificant whenflash exposures are required.

When automatic exposure control is desired for daylight use withoutflash, switch 10 is maintained in the closed position. Thus, theamplifier 2 and filter 3 are short circuited, and the settings are madeas described previously according to the electrical signal resultingfrom the detection of the ambient light. Likewise, means may be providedfor selectively converting the exposure control device to a manualdaylight exposure control system comprising the usual manual overridearrangement known in the art.

In FIG. 2, a graph is shown qualitatively comparing the variousillumination intensities and sequence of operations associated with theinvention. The ambient light level is shown as I Initially, thepreexposure flash is actuated, giving rise to a peak intensity Ip overthe ambient level I The automatic flash exposure control system thenfunctions, and the aperture is set as shown. Thereafter, exposure iscommenced, and the flash illumination attains a peak intensity I abovethe ambient level 1,. The graph shows that the preexposure flashintensity is weak in comparison to the exposure intensity I After theexposure process is complete, the pawl 6 is disengaged from the ratchet7 by known means and the system is reset.

FIG. 2 shows the case when the flash exposure is made immediatelyfollowing the automatic flash exposure control setting. Normally, it isdesirable to make the flash exposure in this manner, especially when thelight level or scene are likely to change. Thus, means may be providedfor having the exposure process automatically follow the setting of theexposure control means. However, the camera mechanism may also be suchthat the exposure can be made at the photographers discretion followingthe setting of the automatic exposure control system, or it may be suchthat the photographer can selectively switch the mechanism to providefor either exposure method.

FIG. 3 showsa graphical comparison of a short duration light preexposureflash accompanied by a conventional exposure flash, and a low intensityelectronic preexposure flash accompanied by an electronic exposure flashwhen these systems are incorporated in the invention. The usualadvantages and shortcomings of each type apply here. The electronicpreexposure flash means are practical when a power supply can beprovided. The electronic preflash is not as bright as the exposure flashsince, as mentioned before, a weak signal is sufficient. As shown in.FIG.v 3, the electronic flash is of much shorter duration than theconventional flash, and reaches its peak intensity almost immediately.

With a short duration light, the preexposure beam can be concentratedboth to increase the electrical signal strength generated in the system,and to reduce the effect of background or uninteresting foregroundduring the setting before exposure. When a beamed spot preflash isemployed, a,

spot 13 in viewfinder reticle 14, as shown in FIG. 4, is superimposedover the desired portion of the viewed subject. The camera operatingbutton (not shown) is then depressed to actuate camera operation withthe actuation of the preexposure flash occuring during part of thepretravel of the shutter release. In this instance, switch may beinitially closed and then opened when the preexposure flash is actuated.In either case, the exposure flash and film exposure can be programmedto follow closely the preexposure flash. If the preexposure flash is notbeamed, i.el in the electronic preflash and flash embodiment, theentire'scene is monitored, and it is therefore unnecessary to composethe scene in the viewfinder following the preexposure flash.

The details of the preferred embodimentof the invention are shown inFIG. 5. This embodiment uses an incandescent short duration light 15which is beamed by lens 16, as indicated in the preceding section. Thegalvanometer 4, diaphragm 5, pawl 6, ratchet 7, aperture 8 and lens 9are shown and described with reference to FIG. 1. Lamp 15 is flashed bypower from capacitor C2 which is charged by battery B through resistorR3. Light reflected from the scene is detected by cadmium sulfide cell Pwhich is restricted in view to detect only the beam emitted by lamp 15to increase the signal to noise ratio. Cell P corresponds to photocell lin FIG. 1 and comprises a photoresistive element. The resistance changein the cell P is reflected in a rapid change in voltage at the junctionof cell P and resistor R,, which then passes through capacitor C], whichfunctions as the filter, to the base of transistor V which operates asthe amplifier. This controls the power from battery B throughgalvanometer 4. Switches S1 and S2 are coupled, as indicated by thedotted line connecting them, to close so that SW2 closes before SW1moves from the CI-IARGE" position to the FIRE position. Switch 10, whichbypasses the above circuitry is normally closed to indicate the level ofambient light. Thus, the requirement for flash exposure is indicatedinitially in a conventional manner by galvanometer needle 17 which maybe viewed in the viewfinder. If such a low level is indicated, thecamera is set for the preflashflash exposure condition by opening switch10 and closing the S1 and S2 switches.

A further aspect of this invention is shown'in FIG. 6 in which thecoupling of focusing means with the camera objective 9 to allow the lensto move into the focus position corresponding to the range of thesubject. Since in most instances all photographic subjects exhibitsubstantially the same reflectance under flash illumination and sincethe intensityvaries with distance, the intensity of the flashillumination which is detected by the photocell circuit is a fairlyaccurate indica tion of the range of the subject. Thus, it is possibleto use the electrical signal resulting from the preexposure flash tofocus the camera lens for the subjects range as well as to set thediaphragm. Hence, in FIG. 6 the diaphragm 5 and galvanometer 4 functionas previously described to effect the correct exposure aperture. In thepresent embodiment, there is provided an arm 18 that moves withdiaphragm member 5. Arm 18 is held in position by pawl 19 and ratchet20, which operate in the manner as described with reference to FIG. 1.Initially,

arm 18 is positioned at the left end of ratchet 20 which comprises themaximum exposure aperture, so that movement of arm 18 toward the otherend of ratchet 20 is not prevented. When the electrical signal receivedby the galvanometer 4 indicates high intensity reflection from thesubject, diaphragm 5 moves in a counterclockwise direction, therebystopping down the lens aperture. Thus, arm 18 moves to the right asshown by the dotted lines towards the NEAR" position, because highintensity reflection to the photocell indicates a close subject range.If the electrical signal indicates low intensity reflection,

diaphragm 5 moves counterclockwise a lesser amount toward arm 18 and islocated at the FAR" position in proportion to the intensity of theelectrical signal. Arm 18 acts to position a focusing gear rack 21 aswill now be shown.

Gear rack 21 engages gear 22 which is a screw mount for the focusinglens 23 of the camera. The rack 21 is biased to the left, i.e. towardsthe farthermost position of arm 18, by spring 24 which is attached tolug 25 on rack 21. In the operation of this arrangement, rack 21 isinitially held to the extreme right by arm 26, which engages lug 25 asshown by the dotted lines. After the exposure setting of diaphragmmember 5 has been made, and arm 18 is positioned according to the rangeof the subject by the engagement of pawl 19 with ratchet 20, arm 26,which pivots about pivot 27, disengages from lug 25 as shown, and rack21 is urged towards arm 18 by spring 24. Movement of rack 21 terminateswhen the rack end contacts arm 18, and is retained in that position byarm 18 and by the force of spring 24. Thus, arm 18 is now locked by pawl19 and rack 21. As the rack 21 makes this movement, it turns the gearedlens screw mount 22, which causes the forward or backward movement offocusing the lens 23. The lens movement is calibrated to maintain itsfocal point on the film plane in accordance with the range of thesubject. After the lens 23 has been located in the correct focusposition, the exposure is made. The operation of arm 26 is preferablyaccomplished automatically in conjunction with the rest of the system,but means may also be provided to operate it manually. Following theexposure, pawl 19 is disengaged from ratchet 20, rack 21 is retracted,and the entire system is reset for the next exposure.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

Iclaim:

1. For use in a camera, an exposure control apparatus for adjusting anexposure varying member in response to preexposure flash illumination,said apparatus comprising:

means for providing preexposure flash illumination of a photographicsubject that is also partially illuminatable by ambient light;

circuit means having an element illuminatable by flash and ambient lightreflected from said subject for generating an intermediate signal as afunction of the total illumination of said element;

filtering circuit means for receiving said intermediate signal and forgenerating an output signal as a function of the proportion of the totalillumination of said element contributed by preexposure flashillumination reflected from the subject; and

means responsive to said output signal for adjusting the exposurevarying member.

2. An exposure control apparatus according to claim 1 wherein saidpreexposure flash is of lower intensity than a subwhen the exposureflash is actuated; and

means for locking said exposure varying member in said adjustedposition.

8. An exposure control apparatus according to claim 7 sequent e posurefl a urther comprising amplifier 5 further comprising means for focusingthe lens of said camera means to amplify the output signal.

3. An exposure control apparatus according to claim 1 wherein saidadjustable exposure means comprises an adjustable diaphragm, and furthercomprising releasable locking means to set the diaphragm at theregulated position.

4. An exposure control apparatus according to claim 1 wherein saidpreexposure flash is an electronic flash.

5. An exposure control apparatus according to claim 1 and furthercomprising means to beam illumination of said preexposure flash.

6. An exposure control apparatus according to claim 1 further comprisingfocusing means for adjusting the position of the camera objective, thefocusing means being responsive to said exposure regulating means.

7. In a camera, an automatic exposure control apparatus comprising:

means for providing a low intensity preexposure flash, said preexposureflash having an intensity proportional to the intensity of a subsequentexposure flash;

circuit means for detecting the reflection of light from the subjectresulting from the preexposure flash, said circuit means comprising: anamplifier, a filter, and a lightresponsive cell, said cell acting inconjunction with the amplifier and filter for generating an electricalsignal proportional to the intensity of the reflection resulting fromthe preexposure flash;

an electromechanical transducer having a mechanical output memberadapted to be deflected an amount proportional to the intensity of theelectrical signal;

an adjustable exposure varying member connected to said mechanicaloutput member for varying exposure according to said deflection toprovide for proper exposure according to the subjects range.

9. An exposure control apparatus according to claim 8 wherein saidfocusing means comprises movable arm positioned by said mechanical meansand moved an amount proportional to the deflection of said mechanicalmeans, means for locking the arm in said position a gear rack, means forurging said gear rack towards said arm such that said rack travels in arestricted path until contacting said arm to position said rack arotatable mount for the objective of the camera engaged by said rack,said mount being turned by said rack when the rack is urged towards saidarm to focus the objective in accordance with the position of said arm.

10. For use in a camera an adjustable exposure control apparatus foradjusting an exposure varying member, said apparatus comprising:

means for generating a preexposure flash to illuminate a subject scenethat is also partially illuminatable by ambient light;

photoresponsive circuit means for detecting light from the scene and forgenerating an intermediate signal as a function of the totalillumination of the scene;

filtering means for receiving said intermediate signal and forgenerating an output signal as a function of the proportion of the totalillumination of the scene by preexposure flash illumination;

means for selectively bypassing said filtering circuit means;

and

transducer means for adjusting the exposure varying member selectivelyin response to said output signal, or in response to said intermediatesignal when said filtering circuit means is bypassed.

